US7321581B2ExpiredUtilityA1
Method of double weighting parallel interference cancellation
Est. expiryOct 9, 2021(expired)· nominal 20-yr term from priority
H04B 2001/71077H04B 1/71075
52
PatentIndex Score
5
Cited by
9
References
10
Claims
Abstract
A method for double weighting parallel interference cancellation in CDMA mobile communication system, integrates ideas of both partial weighting method and weighting method based on Bayes rule. When making a decision on each symbol of the user, calculating reliability coefficient of a decision result on the symbol of the user according to the weighting algorithm based on Bayes rule; weighting regenerated signal of the symbol of the user with the reliability coefficient. During process of MAI estimating and removing, obtaining the MAI on the expected user from weighted regenerated signal of other users in chip level; and then setting a weight value, weighting the MAI with the weight value. Finally, removing weighted MAI from received signal, which means partially removing MAI produced by other users on the expected user. At the same time, the present invention also discloses a double weighting PIC method with simplified algorithm, which transfers weighting in chip level to weighting in symbol level, replacing a Hyperbolic tangent decision with a piecewise linear decision method or a look-up table method.
Claims
exact text as granted — not AI-modified1. A double weighting parallel interference cancellation method that can be used in a CDMA mobile communication system, comprises:
(a) Making a multi-path despreading, channel estimation and a multi-path combining on an input signal of a user by a RAKE receiver;
(b) Making a hard decision on a result of the multi-path combining;
(c) Calculating a reliability coefficient for a result of the hard decision of each symbol by the multi-path combining result and a value of the channel estimation;
(d) Regenerating a weighted signal in chip level for the user by the hard decision result, the reliability coefficient and the channel estimation value;
(e) Estimating a multiple access interference on each user by the weighted regenerated signal in chip level inputted in parallel of each user, and setting a weight value for a interference cancellation in different stages, weighting the multiple access interference on a expected user;
(f) Subtracting the weighted multiple access interference on the expected user from a base band signal of a received signal, and obtaining an output signal of the said expected user, which is also an input signal of the said expected user in the next stage parallel interference cancellation.
2. The double weighting parallel interference cancellation method according to claim 1 , comprises, if the said input signal of user i in the kth stage parallel interference cancellation is expressed as r i (k) (t),
In step (a), calculating the said multi-path combining result of user i by a formula
Y
i
(
m
)
(
k
)
=
Re
{
y
i
(
m
)
(
k
)
}
,
which can be expressed as
Y
i
(
m
)
(
k
)
=
μ
i
a
i
(
m
)
+
n
i
,
where, n i is a Gaussian White Noise, which is subject to a normal distribution of
N
(
0
,
σ
i
2
)
,
σ
2
is a noise power of
n
i
,
a
i
(
m
)
is the mth symbol of user i, whose value is +1 or −1, μ i is a real number that is related with channel fading;
In step (b), calculating the said hard decision result of the mth symbol of user i by a formula
a
^
i
(
m
)
(
k
)
=
sgn
(
Y
i
(
m
)
(
k
)
)
;
In step (c), calculating the said reliability coefficient of the said decision result on the mth symbol of user i by
f
i
(
m
)
(
k
)
=
tanh
{
w
μ
i
Y
i
(
m
)
(
k
)
σ
i
2
}
,
where, w is a positive real number;
In step (d), calculating the said weighted regenerated signal of user i in chip level by a formula
g
i
(
k
)
(
t
)
=
∑
l
=
1
L
A
il
∑
n
=
-
∞
∞
f
i
(
n
)
(
k
)
a
^
i
(
n
)
(
k
)
p
(
t
-
nT
b
-
τ
il
)
c
i
(
t
-
τ
il
)
,
where, A il is a estimation value of a il √{square root over (P i )}, a il refers to a channel fading value of user i in the path l, p i is a power of user i;
In step (e), calculating the said multiple access interference estimation of user i by a formula
I
i
(
k
)
=
∑
j
=
1
,
j
≠
i
N
g
j
(
k
)
(
t
)
;
Assuming the said weight value of the kth stage parallel interference cancellation is p (k) , then calculating the said output signal of user i in step (f) by a formula
r
i
(
k
+
1
)
(
t
)
=
r
(
t
)
-
p
(
k
)
I
^
i
(
k
)
,
where, r(t) is the said base band signal of the said received signal.
3. The double weighting parallel interference cancellation method according to claim 2 , wherein step (c) of calculating the said reliability coefficient of the said decision result on the mth symbol of user i comprises, replacing the said Hyperbolic tangent decision with a piecewise linear decision, which means approaching a Hyperbolic tangent function tanh(x) with a piecewise linear decision function L(x), a expression of the piecewise linear decision function L(x) is:
1
,
x
>
θ
L
(
x
)
=
{
L
q
(
x
)
,
x
∈
[
x
q
-
1
,
x
q
]
-
L
q
(
-
x
)
,
x
∈
[
-
x
q
,
-
x
q
-
1
]
.
-
1
,
x
<
-
θ
4. The double weighting parallel interference cancellation method according to claim 2 , wherein step (c) of calculating the said reliability coefficient of the said decision result on the mth symbol of user i comprises, replacing the said Hyperbolic tangent decision with a look-up table method, which means approaching a Hyperbolic tangent function tanh(x) with a decision function T(x) of the look-up table method, a expression of the said decision function T(x) of the look-up table method is:
1
,
x
>
θ
T
(
x
)
=
{
tanh
(
x
q
-
1
+
x
q
2
)
,
x
∈
[
x
q
-
1
,
x
q
]
-
tanh
(
x
q
-
1
+
x
q
2
)
,
x
∈
[
-
x
q
,
-
x
q
-
1
]
.
-
1
,
x
<
-
θ
5. The double weighting parallel interference cancellation method according to claim 1 , wherein step (e) comprises, setting the different weight value p (k) for the interference cancellation in different stages, wherein p (1) <p (2) . . . <p (k) . . . <p (S) , where, k is the kth stage of the interference cancellation, and S is a stage number of the interference cancellation.
6. A double weighting parallel interference cancellation method that can be used in CDMA mobile communication system, comprises:
(a) Making a multi-path despreading, channel estimation and a multi-path combining on an input signal of a user by a RAKE receiver;
(b) Making a soft decision on a result of the multi-path combining and a value of the channel estimation;
(c) Setting a weight value for the soft decision in different stages, and weighting the soft decision in symbol level;
(d) Regenerating a weighted signal of the user in chip level by the weighted soft decision result and the channel estimation value;
(e) Estimating multiple access interference on each user by the weighted regenerated signal in chip level inputted in parallel of each user;
(f) Subtracting the multiple access interference on an expected user from a base band signal of a received signal, and obtaining an output signal of the expected user, which is also an input signal of the said expected user in the next stage of parallel interference cancellation.
7. The double weighting parallel interference cancellation method according to claim 6 , comprises, if the said input signal of user i in the kth stage parallel interference cancellation is expressed as
r
i
(
k
)
(
t
)
,
In step (a), calculating the said multi-path combining result of user i by a formula
Y
i
(
m
)
(
k
)
=
Re
{
y
i
(
m
)
(
k
)
}
,
which can be expressed as
Y
i
(
m
)
(
k
)
=
μ
i
a
i
(
m
)
+
n
i
,
where, n i is a Gaussian White Noise, which is subject to a normal distribution of
N
(
0
,
σ
i
2
)
,
σ
2
is a noise power of
n
i
a
i
(
m
)
is the mth symbol of user i, whose value is +1 or −1, μ i is a real number that is related with channel fading;
In step (b), expressing the said soft decision of the said multi-path combining result for user i as
ξ
i
(
m
)
(
k
)
=
f
i
(
m
)
(
k
)
a
^
i
(
m
)
(
k
)
,
calculating the said soft decision by a formula
f
i
(
m
)
(
k
)
a
^
i
(
m
)
(
k
)
=
tanh
{
w
μ
i
Y
i
(
m
)
(
k
)
σ
i
2
}
,
where, W is a positive real number,
a
^
i
(
m
)
(
k
)
is a soft decision result for the mth symbol of user
i
,
f
i
(
m
)
(
k
)
is a reliability coefficient of
a
^
i
(
m
)
(
k
)
;
Assuming the said weight value of the said soft decision in the kth stage is p (k) , and then in step (c) calculating the said weighted soft decision of user i in symbol level by a formula
ρ
i
(
m
)
(
k
)
=
ζ
i
(
m
)
(
k
)
·
p
(
k
)
;
In step (d), calculating the said weighed regenerated signal in chip level of user i by a formula
g
i
(
k
)
(
t
)
=
∑
l
=
1
L
A
il
∑
n
=
-
∞
∞
ρ
i
(
n
)
(
k
)
a
^
i
(
n
)
(
k
)
p
(
t
-
nT
b
-
τ
il
)
c
i
(
t
-
τ
il
)
,
where, A il is a estimation value of a il √{square root over (P i )}, a il refers to a channel fading value of user i in the path l, and p i is a power of user i;
In step (e), calculating the said multiple access interference on user i by a formula
I
^
i
(
k
)
=
∑
j
=
1
,
j
≠
i
N
g
j
(
k
)
(
t
)
;
In step (f), calculating the said output signal of user i by a formula
r
i
(
k
+
1
)
(
t
)
=
r
(
t
)
-
I
^
i
(
k
)
,
where, r(t) is the said base band signal of the said received signal.
8. The double weighting parallel interference cancellation method according to claim 7 , wherein step (b) of making the said soft decision of the said multi-path combining result for user i comprises, replacing the said Hyperbolic tangent decision with a piecewise linear decision, which means approaching a Hyperbolic tangent function tanh(x) with a piecewise linear decision function L(x), a expression of the piecewise linear decision function L(x) is:
L
(
x
)
=
{
1
,
x
>
θ
L
q
(
x
)
,
x
∈
[
x
q
-
1
,
x
q
]
-
L
q
(
-
x
)
,
x
∈
[
-
x
q
,
-
x
q
-
1
]
-
1
,
x
<
-
θ
.
9. The double weighting parallel interference cancellation method according to claim 7 , wherein step (b) of making the said soft decision of the said multi-path combining result for user i comprises, replacing the said Hyperbolic tangent decision with a look-up table method, which means approaching a Hyperbolic tangent function tanh(x) with a decision function T(x) of the look-up table method, a expression of the said decision function T(x) of the said look-up table method is:
T
(
x
)
=
{
1
,
x
>
θ
tanh
(
x
q
-
1
+
x
q
2
)
,
x
∈
[
x
q
-
1
,
x
q
]
-
tanh
(
x
q
-
1
+
x
q
2
)
,
x
∈
[
-
x
q
,
x
q
-
1
]
-
1
,
x
<
θ
.
10. The double weighting parallel interference cancellation method according to claim 6 , wherein step (c) comprises, setting the different weight value p (k) for the soft decision in different stages, wherein p (1) <p (2) . . . <p (k) . . . <p (S) , where, k is the kth stage of the interference cancellation, and S is a stage number of the interference cancellation.Cited by (0)
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